Spectacular radio bursts observed in dormant black holes

Des trous noirs "zombies"

What happens to a star that gets too close to a hungry black hole? She ends up with “Spaghetti”., in other words, has been extended to produce large pieces of plasma in the form of the famous Italian pasta. This “spaghettiization” still has a scientific nameWave breaking event (TDE) and one of the most violent processes in the universe.

Due to the black hole’s powerful gravitational pull, the collapsed star’s debris emits a brilliant glow before it disappears beyond the object’s event horizon. This luminous feast can continue for months before the black hole returns to a peaceful state of sleep. But sometimes this sleeping position is not so restful.

Black holes move away from their digestion

Several observations have revealed that black holes can wake up and eject matter and energy, sending bursts of radio waves toward Earth months or even after the initial TDE. “How incredibly unusual [ces événements]These objects came back to life like zombies.”Explains Enrico Ramirez-Ruiz, an astrophysicist at the University of California, Santa Cruz, citing Science. “It really challenges the paradigm.”

Until recently, all recorded ejections as part of dozens of known TDEs, detected by optical light or X-rays emitted by the black hole’s jet material, occurred very shortly after the black hole shredded its food. But with the development of observations in the field of radio waves, hitherto unknown behaviors have been observed in black holes.

In February 2021, Assaf Horesh, an astrophysicist at the Hebrew University of Jerusalem, He discovered a radio burst six months after the initial TDE. On June 30 of the same year, history repeated itself: Yvette Sentus, an astronomer at the Harvard Center for Astrophysics and the Smithsonian Center, Another delayed explosion was discovered. Using multiple telescopes, she and her team determined that there was a rapid peak in radio activity more than two years after the black hole’s feeding! Scientists were confused, to say the least.

A disk in the middle

Today, a third example has been added to this list: while reanalyzing a previously observed TDE, Assaf Horesh’s student Itai Sfaradi claims to have recorded delayed radio emissions in conjunction with an X-ray flare. So-called X-ray binaries — where star-sized black holes suck gas from a pair of stars — suggest the mechanisms may be coupled. His works have been publishedAstrophysical Journal Dated July 10, 2022.

Researchers are now proposing a hypothesis to explain these delayed flares: displacements of the black hole’s accretion disk fuel the explosions of X-ray binaries, which can also occur in supermassive black holes months after they are consumed. Gas from a torn star builds up slowly over time, making the accretion disk cooler and thinner. The latter, “weakened”, would then allow projections of matter to travel into space, where they would collide with the surrounding gas, producing the famous radio bursts. Overall, the accretion disk will still be dense enough to support the jets, but somewhat less likely to reabsorb the generated radio waves.

Large-scale radio surveys will be needed to confirm this scenario. According to Enrico Ramírez-Ruiz, the question is still raised ScienceThe discovery of a larger population of these “zombie” TDEs would enable the behavior of black holes to be studied in more detail over a wide range of conditions. “Black Hole Gastronomy Really Offers a New Playground”, He concludes.

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